The present invention relates to an apparatus for joining together substrates, which have an inner hole, to form a substrate disk, and includes an expandable element that can be introduced into the inner hole of at least two superimposed substrates.
Such an apparatus for the joining together of disks to form a CD or DVD is known, for example, from U.S. Pat. No. 4,877,875. With this known apparatus, a centering pin is provided that prior to the joining together of the substrates is introduced into the respective inner hole of the substrates in order to center them relative to one another. During the joining together, the substrates are rotated in order to uniformly distribute an adhesive material that is disposed between them. To prevent a slippage between the substrates, which would adversely affect the joining-together process, the substrates must be rotated synchronously. With the known apparatus this is achieved via a frictional connection between the substrates, in that the substrates are pressed so strongly against one another that they rotate in common.
As a result of this pressing together of the substrates, however, there results the problem that the substrates must already be brought into contact prior to a uniform distribution of the adhesive between them, which adversely affects the distribution of the adhesive. Furthermore, all mechanical components of the apparatus must have such a strong design that they can resist the mechanical loading during the pressing together, which leads to high costs for the apparatus. Furthermore, there is the danger that air penetrates via the respective inner holes into the gap formed between the substrates, as a result of which bubbles can result on the inner edge of the adhesive.
From EP 0 833 315 A an apparatus of the aformentioned type is furthermore known.
Proceeding from the known apparatus, it is an object of the present invention to provide an apparatus for the joining together of substrates, which have an inner hole, to form a substrate disk, with such apparatus ensuring in a straightforward and economical manner a simultaneous rotation of both substrates during the adhesion process.